XTemplate is available as a property(config) for many components eg tpl for component and itemTpl for Dataview.

@bharatn writes at it is possible for custom variables. So if I would like to use XTemplate for itemTpl, so what should I do?
To overload the component, to set template with list.setTpl() or is there another better solution?

sencha generates files and you cannot change them, you can only make overrides.
Generally, it doesnt matter what you do with generated files bcs they are regenerated(from metadata files) each time you save project.